1. Field of the Invention
The present invention relates to transferring wafers among modules of semiconductor processing equipment, and more particularly to placing accurately each wafer, with the support blade that carries the wafer, inside the modules.
2. Description of the Related Art
In the manufacture of semiconductor devices, process chambers are interfaced to permit transfer of wafers or substrates, for example, between the interfaced chambers. Such transfer is via transfer modules that move the wafers, for example, through slots or ports that are provided in the adjacent walls of the interfaced chambers. Transfer modules are generally used in conjunction with a variety of wafer processing modules (PM), which may include semiconductor etching systems, material deposition systems, and flat panel display etching systems.
A vacuum transfer module (VTM) may be physically located between one or more clean room storage facilities where wafers are stored, and multiple wafer processing modules where the wafers are actually processed, e.g., etched or have deposition performed thereon. In this manner, when a wafer is required for processing, a robot arm located within the transfer module may be employed to retrieve a selected wafer from storage and place the wafer into one of the multiple processing modules.
Sensors at each of the facets of each station have been used to increase the accuracy of wafer placement inside each station. However, the accuracy for placing wafers suffers due to multiple factors. For example, the position of the sensors may not be perfect and small deviations in sensor location result in defects when calculating wafer position. In addition, the robot transporting the wafer may not be in the exact place where the system believes that the robot is, which creates another source for errors. Still yet, the robots that transfer the wafers often have two arms to increase speed and flexibility in the system. In practice, there are operational differences between using one robot arm or the other, producing different results according to which robot arm picks up, or places the wafer when transporting the wafer. Additionally, existing methods are susceptible to operator's errors and are not automated, requiring long calibration times.
It is in this context that embodiments of the invention arise.